The Biomimicry Manual: What Can Sloths Teach Us About Energy Efficiency?

It’s a scientific fact that there’s nothing cuter than a baby sloth in a bucket. But even if Facebook ‘likes’ turn out not to correlate with biological fitness, sloths are a runaway success by any measure. Well, maybe not so much ‘runaway.’ But it’s certainly true they’re not going anywhere. Sloths have an outstanding survival strategy, as their unexpectedly high density in South and Central American tropical forests attests. In some areas, sloths consume half the energy and make up two-thirds of mammalian biomass. That’s a lot of sloths. But it’s hard to see them because they hardly move—their leafy diets just don’t provide enough energy for them to monkey around. How do they succeed on such meager rations? Simple. They are consummate energy misers. Can humans learn something about conserving energy from the sloth? Read today’s entry of The Biomimicry Manual to find out!

The sloth spends his whole life browsing in the trees, and he’s built perfectly for it. In fact, he can’t even stand up on the ground because his hands and feet are essentially coat-hangers. He is designed to do one thing: hang upside-down from a horizontal tree branch. His body is designed to resist tension forces, not compression. He’s a great natural model for hanging roofs, gardens, and bridges. Pretty much anything that hangs.

He lives on leaves, which are plentiful and easy to find but hard to digest and give little energy or nutrition. The solution? A cow-like, multi-chambered, slow-acting stomach full of leaf-eating bacteria. They also have an extremely low metabolic rate (less than half of what you’d expect for his size). While most mammals keep their body temperature around 100 degrees, the sloth stays well below 90. In fact, even though he makes his home in warm, wet tropical forests, he has to work to keep warm. He sunbathes high in the canopy, sleeps in a compact ball to conserve heat, and cuddles up in a dense fur coat.

Which brings us to the sloth’s other brilliant energy-saving strategy: collaboration. There’s a whole ecosystem thriving in sloth fur. One sloth is a playground for moths, beetles, cockroaches, fungi, and algae. In one case, 950 beetles were found living on a single sloth. All these creatures work together, exchanging nutrients, energy, and “surfing for free” on each other’s special talents.

For instance, each individual hair on a sloth has a special groove which absorbs water like a sponge. Certain blue-green algae love this. They multiply in the rainy season, turning the sloth a nice shade of green, perfectly hiding him from hungry harpy eagles. The sloth licks the algae for a nutrient boost—like a hippie with a shot of wheatgrass—and even absorbs it through the skin. The algae is passed directly from mom to baby sloth, and each species of algae is only found on a unique population of sloths.

In fact, most organisms living on any given sloth species have been evolving separately just as long as the sloths themselves have, about 20 million years. These are a pretty specialized bunch of critters. For example, the sloth moth only lays its eggs in sloth dung. Since a sloth spends most of its life in one single tree, he feels compelled to descend once a week to dig a hole and carefully fertilize it. The moth takes this opportunity to jump off and lay her eggs, then jump back on for the ride up the tree. The eggs hatch, the caterpillars metamorphosize, and the new moths fly off to find new sloths.

When organisms cooperate, it’s a win-win for everyone. This also reminds me of the Kalundborg Industrial Ecosystem in Denmark, where a power plant, oil refinery, pharmaceutical plant, plasterboard factory, an enzyme manufacturer, a waste company and the city all trade and share byproducts and heat emissions. Why shouldn’t our human industrial ecosystem be more sloth-like, with one species’ waste becoming food for another, reducing raw materials, pollution, and waste? It’s another great idea from Mother Nature. Just like baby sloths in a bucket.